1. Field of the Invention
The present invention relates to a semiconductor device, and more specifically to a thinned resin encapsulated semiconductor device and a method for manufacturing the same.
2. Description of Related Art
Referring to FIG. 1, there is shown a pattern diagram of one example of a conventional lead frame for a semiconductor device. The shown lead frame is generally designated with Reference Numeral 1, and includes a rectangular island 2 to support a semiconductor chip (not shown) thereon, and a hanger lead 3 outwardly extending from each of four comers of the rectangular island 2 to an outer frame 1A of the lead frame so that the rectangular island 2 is supported by the frame of the lead frame. The lead frame 1 also includes a number of inner leads 4 extending from the outer frame 1A of the lead frame near to a periphery of the rectangular island 2. These inner leads are to be electrically connected to external electrodes formed on the semiconductor chip.
The conventional lead frame as mentioned above has been designed on the condition that the whole of a bottom surface the semiconductor chip is contacted to the island. Therefore a minimum size of the island is restricted by the size of the semiconductor chip to be put on the island. Namely, EQU Size of Island&gt;Size of Semiconductor Chip (1)
On the other hand, a maximum size of the island is restricted from the necessity of wiring-bonding between the external electrodes of the semiconductor chip and the inner leads in order to transmit signals and electric power between the semiconductor chip and a device external to the semiconductor chip. Therefore, the following condition is required to be fulfilled: EQU Size of Island&lt;Size of Semiconductor Chip+Bonding Enable Length.times.2 (2)
In the prior art. in order to fulfill both the above mentioned conditions (1) and (2), even if the shape of the outer leads is the same, if the size of the semiconductor chip is different, it has been required to modify the size of the island on the basis of the size of the semiconductor chip. Therefore, in the case that semiconductor devices having the same shape of outer leads but different sizes of semiconductor chips are to be manufactured, it is necessary to prepare a plurality of different kinds of lead frames.
For example, in order to assemble the semiconductor device by using the conventional lead frame, a semiconductor chip is die-bonded on the island 2 of the lead frame 1, and a wire-bonding is carried out between the electrodes of the semiconductor chip and the inner leads 4 of the lead frame 1, and thereafter, the semiconductor chip, the island 2, the hanger leads 3 and the inner leads 4 and the bonding wires are encapsulated with a molding resin, and a lead frame portion extending outward from the encapsulating molded resin is cut out.
On the other hand, it recently becomes important to miniaturize and thin the semiconductor device in order to realize a high density packaging. For example in the case of thinning the semiconductor device, only the package (namely, encapsulating molded resin portion) is thinned without modifying the lead frame. In this case, a resin-to-metal proportion (proportion of a resin portion to a metal portion (lead frame, etc) in the package becomes small as a matter of course. As a result, when the finished semiconductor device is put under a heat cycle test, because a heat stress results from a large difference in thermal expansion coefficient between the resin and the metal, the probability of generating of package crack defect increases.
As mentioned above in order to manufacture various semiconductor devices it was necessary to prepare a plurality of different kinds of lead frames in accordance with different sizes of semiconductor chips. Nevertheless, when the chip size is suddenly changed because of change in design of the semiconductor devices, it is often difficult to immediately supply necessary lead frames fitted to the changed chip size. On the other hand, for efficient production of semiconductor devices, it is necessary to anticipate a production plan and to order the anticipated kinds of lead frames. However, this approach cannot quickly cope with an abrupt increase or decrease in demand, resulting in increased quantities of lead frames in stock.